Surface plasmon resonance biosensor based on Au nanoparticle in titania sol–gel membrane

An Unconventional Immunosensor for Biomolecule Detection via Nonspecific Gold Nanoparticle-Antibody Interactions

Immunogold, that is, gold nanoparticles (AuNPs) conjugated with biomolecules such as antibodies and peptides, have been widely used to construct sandwiched immunosensors for biodetection. Two main challenges in these immunoassays are difficulties in finding and validating a suitable antibody, and the nonspecific interaction between the substrate and immunogold, which lowers the detection sensitivity and even causes false results. To avoid these issues, we took advantage of the nonspecific interaction between AuNPs and capture antibodies and proposed a new sensing mechanism. That is, after the capture of analyte targets by the capture antibodies on the substrate, AuNPs of certain chemical functionality would preferably bind to the free capture antibodies. Consequently, the amount of deposited AuNPs will inversely depend on the concentration of the analytes. As a proof-of-concept, we designed a mass-based sensor where anti-IgG antibodies were coated on a quartz crystal microbalance substrate. After IgG was introduced, tannic acid-capped AuNPs were applied to bind with the free anti-IgG antibody molecules. A frequency change (Δf) of the quartz substrate was induced by the increased mass loading. To further amplify the loading mass, an Ag enhancer solution was added, and Ag growth was catalyzed by the bound AuNPs. The Δf response showed a concentration-dependent decrease when increasing IgG concentration with a detection limit of 2.6 ng/mL. This method relies on the nonspecific interaction between AuNPs and anti-IgG antibodies to realize sensitive detection of IgG and eliminates the use of detection antibodies. The concept is an alternative to many existing immunoassay technologies.

Polyvinylpyrrolidone-coated gold nanoparticles inhibit endothelial cell viability, proliferation, and ERK1/2 phosphorylation and reduce the magnitude of endothelial-independent dilator responses in isolated aortic vessels

Background

Gold nanoparticles (AuNPs) demonstrate clinical potential for drug delivery and imaging diagnostics. As AuNPs aggregate in physiological fluids, polymer-surface modifications are utilized to allow their stabilization and enhance their retention time in blood. However, the impact of AuNPs on blood vessel function remains poorly understood. In the present study, we investigated the effects of AuNPs and their stabilizers on endothelial cell (EC) and vasodilator function.

Materials and methods

Citrate-stabilized AuNPs (12±3 nm) were synthesized and surface-modified using mercapto polyethylene glycol (mPEG) and polyvinylpyrrolidone (PVP) polymers. Their uptake by isolated ECs and whole vessels was visualized using transmission electron microscopy and quantified using inductively coupled plasma mass spectrometry. Their biological effects on EC proliferation, viability, apoptosis, and the ERK1/2-signaling pathway were determined using automated cell counting, flow cytometry, and Western blotting, respectively. Endothelial-dependent and independent vasodilator functions were assessed using isolated murine aortic vessel rings ex vivo.

Results

AuNPs were located in endothelial endosomes within 30 minutes’ exposure, while their surface modification delayed this cellular uptake over time. After 24 hours’ exposure, all AuNPs (including polymer-modified AuNPs) induced apoptosis and decreased cell viability/proliferation. These inhibitory effects were lost after 48 hours’ exposure (except for the PVP-modified AuNPs). Furthermore, all AuNPs decreased acetylcholine (ACh)-induced phosphorylation of ERK1/2, a key signaling protein of cell function. mPEG-modified AuNPs had lower cytostatic effects than PVP-modified AuNPs. Citrate-stabilized AuNPs did not alter endothelial-dependent vasodilation induced by ACh, but attenuated endothelial-independent responses induced by sodium nitroprusside. PVP-modified AuNPs attenuated ACh-induced dilation, whereas mPEG-modified AuNPs did not, though this was dose-related.

Conclusion

We demonstrated that mPEG-modified AuNPs at a therapeutic dosage showed lower cytostatic effects and were less detrimental to vasodilator function than PVP-modified AuNPs, indicating greater potential as agents for diagnostic imaging and therapy.

Detection of Bacillus thuringiensis Cry1Ab protein based on surface plasmon resonance immunosensor

Two novel surface plasmon resonance immunosensors were fabricated for detection of the Bacillus thuringiensis Cry1Ab protein and to demonstrate their performance in analyzing Cry1Ab protein in crop samples. Sensor 2 was modified by 1,6-hexanedithiol, Au/Ag alloy nanoparticles, 3-mercaptopropionic acid, and protein A (or not [sensor 1]), with Cry1Ab monoclonal antibody. As a result, both of the immunosensors exhibited satisfactory linear responses in the Cry1Ab protein concentration ranges of 10 to 500ngml(-1) and 8 to 1000ngml(-1), and the detection limits were 5.0 and 4.8ngml(-1), respectively. The immunosensors possessed good specificity and acceptable reproducibility. In addition, crop samples could be analyzed after a simple treatment. The transgenic crops could be easily identified from the conventional ones by the two immunosensors.

Preparation of graphene oxide-based surface plasmon resonance biosensor with Au bipyramid nanoparticles as sensitivity enhancer

A sensitive and selective wavelength-modulation surface plasmon resonance (SPR) biosensor based on graphene oxide (GO) and Au bipyramids (AuBPs) is reported for determination of bovine IgM. GO sheets with lengths of 100-300 nm are synthesized and assembled on amine-modified Au film. The large surface area and abundant functional groups of GO allow the efficient immobilization of antibody. AuBPs are nanoparticles with a penta-twinned crystal structure, which have a sharp localized surface plasmon resonance (LSPR) band because of their high monodispersity. In the optimal conditions, the GO-based biosensor with AuBPs as sensitivity enhancers shows a satisfactory response to bovine IgM in the concentration range of 0.03-32 μg mL(-1). For contrast, traditional biosensor, GO-based biosensor and GO-based biosensor with Au nanorods (AuNRs) as sensitivity enhancers for antigen detection were also investigated. Consequently, the as-prepared GO sheets function as promising support for antibody and GO-based SPR biosensor using AuBPs as enhancers has the highest sensitivity among the four types of biosensors.

Inactivation of microbial infectiousness by silver nanoparticles-coated condom: a new approach to inhibit HIV- and HSV-transmitted infection

Recent research suggests that today’s condoms are only 85% effective in preventing human immunodeficiency virus (HIV) and other sexually transmitted diseases. In response, there has been a push to develop more effective ways of decreasing the spread of the disease. The new nanotechnology-based condom holds the promise of being more potent than the first-generation products. The preliminary goal of this study was to develop a silver nanoparticles (Ag-NPs)-coated polyurethane condom (PUC) and to investigate its antimicrobial potential including the inactivation of HIV and herpes simplex virus (HSV) infectiousness. The Ag-NPs-coated PUC was characterized by using ultraviolet-visible spectrophotometry, Fourier transform-infrared spectroscopy, high-resolution scanning electron microscopy, and energy-dispersive analysis of X-ray spectroscopy. Nanoparticles were stable on the PUC and not washed away by water. Morphology of the PUC was retained after coating. The NP binding is due to its interaction with the nitrogen atom of the PUC. No significant toxic effects was observed when human HeLa cells, 293T and C8166 T cells were contacted to Ag-NPs-coated PUC for three hours. Interestingly, our results demonstrated that the contact of the Ag-NPs-coated PUC with HIV-1 and HSV-1/2 was able to efficiently inactivate their infectiousness. In an attempt to elucidate the antiviral action of the Ag-NPs, we have demonstrated that the anti-HIV activity was primarily mediated by the Ag-NPs, which are associated with the PUC. In addition, the data showed that both macrophage (M)-tropic and T lymphocyte (T)-tropic strains of HIV-1 were highly sensitive to the Ag-NPs-coated PUC. Furthermore, we also showed that the Ag-NPs-coated PUC was able to inhibit the growth of bacteria and fungi. These results demonstrated that the Ag-NPs-coated PUC is able to directly inactivate the microbe’s infectious ability and provides another defense line against these sexually transmitted microbial infections.

Surface plasmon resonance biosensors incorporating gold nanoparticles

SPR biosensing is increasingly popular for the detection of a multitude of biomolecules. It offers label-free detection and study of proteins, nucleic acids, and other biomolecules in real time. A recent trend involves incorporation of AuNPs, either within the sensing surface itself or as signal enhancing tagging molecules. The importance of AuNP and detecting agent spacing is described and techniques using macromolecular spacing aids are highlighted. Recent methods to enhance SPR detection capabilities using gold nanoparticles are reviewed, as well as device fabrication and the results of incorporation. SPR detection is a highly versatile method for the detection of biomolecules and, with the incorporation of AuNPs, shows promise in extending it to a number of new applications.

Embedded layer of Ag nanoparticles prepared by a combined PECVD/PVD process producing SiOxCy-Ag nanocomposite thin films

Structural properties of SiO(x)C(y)-Ag nanocomposite thin films prepared by a dual process PVD-PECVD in the same reactor have been investigated. The experimental results have demonstrated the influence of a PECVD process carried out at room temperature for the growth of a dielectric matrix on the size and the distribution density of Ag nanoparticles (NPs) deposited beforehand by magnetron sputtering. The plasma during the growth of the encapsulation SiO(x)C(y) layer caused a diffusion of silver from NPs through the SiO(x)C(y) matrix associated with a decrease in the average size of nanoparticles and an increase of their distribution density. Silver diffusion is blocked at a barrier interface to form a buried layer of individual Ag NPs which, for instance, can find plasmonic applications. Silver also diffuses toward the outer surface inducing antibacterial properties. In both cases initial Ag NPs act as reservoirs for multifunctional properties of advanced nanostructured films.